1. Field of the Invention
Aspects of the present invention relate to an organic light emitting display device, and more particularly to an organic light emitting display device capable of ensuring the drive stability.
2. Description of the Related Art
In recent years, various light emitting diode display devices that are lighter and smaller than a cathode ray tube (CRT) have been developed. Such flat display panels include liquid crystal display devices (LCDs), field emission display devices (FEDs), plasma display panels (PDPs), organic light emitting display devices, etc.
Among the flat display panels, the organic light emitting display device displays an image by using organic light emitting diodes (OLEDs) that generate light by recombining of electrons and holes. Organic light emitting display devices have advantages such as a rapid response time and low power consumption.
FIG. 1 is a circuit diagram showing a pixel in a conventional organic light emitting display device.
Referring to FIG. 1, the pixel 4 of the organic light emitting display device includes an organic light emitting diode (OLED) and a pixel circuit 2 coupled to a data line (Dm) and a scan line (Sn) to control the organic light emitting diode (OLED).
An anode electrode of the organic light emitting diode (OLED) is coupled to the pixel circuit 2, and a cathode electrode of the organic light emitting diode (OLED) is coupled to a second power source (ELVSS). Such organic light emitting diodes (OLEDs) generate light with a predetermined brightness corresponding to an electric current supplied from the pixel circuit 2.
The pixel circuit 2 controls the amount of a current supplied to the organic light emitting diode (OLED) to correspond to a data signal supplied to the data line (Dm) when a scan signal is supplied to the scan line (Sn). For this purpose, the pixel circuit 2 includes a second transistor (M2) coupled between a first power source (ELVDD) and the organic light emitting diode (OLED), a second transistor (M2), a first transistor (M1) coupled between the data line (Dm) and the scan line (Sn), and a storage capacitor (Cst) coupled between a gate electrode and a first electrode of the second transistor (M2).
A gate electrode of the first transistor (M1) is coupled to the scan line (Sn), and a first electrode of the first transistor (M1) is coupled to the data line (Dm). A second electrode of the first transistor (M1) is coupled to one side terminal of the storage capacitor (Cst). Here, the first electrode is set as either of a source electrode or a drain electrode, and the second electrode is set as an electrode that is different from the first electrode. For example, when the first electrode is set as a source electrode, the second electrode is set as a drain electrode. When a scan signal is supplied from the scan line (Sn), the first transistor (M1) coupled to the scan line (Sn) and the data line (Dm) is turned on to supply a data signal supplied from the data line (Dm) to the storage capacitor (Cst). In this case, the storage capacitor (Cst) stores a voltage corresponding to a data signal.
A gate electrode of the second transistor (M2) is coupled to one side terminal of the storage capacitor (Cst), and a first electrode of the second transistor (M2) is coupled to the other side terminal of the storage capacitor (Cst) and the first power source (ELVDD). A second electrode of the second transistor (M2) is coupled to an anode electrode of the organic light emitting diode (OLED). The second transistor (M2) controls the amount of a current so that the current corresponds to a voltage value stored in the storage capacitor (Cst). The current flows from the first power source (ELVDD) to the second power source (ELVSS) via the organic light emitting diode (OLED). In this case, the organic light emitting diode (OLED) generates light corresponding to the amount of current capacity supplied from the second transistor (M2).
However, the pixel 4 of the conventional organic light emitting display device has a problem, in that it is difficult to display an image with a desired brightness due to the non-uniformity in a threshold voltage of the second transistor (M2) and the degradation of the organic light emitting diode (OLED). In order to solve the above problem, there has been proposed a pixel structure in which each of the pixels includes a plurality of transistors to compensate for the non-uniformity in the threshold voltage and/or the degradation of the organic light emitting diode (OLED). However, when each of the pixels includes a plurality of the transistors, the number of pixels to which some scan lines are coupled is different from the number of pixels to which other scan lines are coupled. In such a situation, the drive stability may deteriorate because various scan lines will have a non-uniform load.